On December 10, 2015 5:02:27 AM GMT+01:00, Michael Paquier <michael.paquier@gmail.com> wrote:
>On Wed, Dec 9, 2015 at 9:07 PM, Andres Freund <andres@anarazel.de>
>wrote:
>> On 2015-12-09 21:03:47 +0900, Michael Paquier wrote:
>>> Oh, OK. I didn't read though your lines correctly. So you basically
>>> mean that we would look at the init files that are on disk, and
>check
>>> if they are empty. If they are, we simply use XLogReadBufferExtended
>>> to fetch the INIT_FORKNUM content and fill in another buffer for the
>>> MAIN_FORKNUM. More or less right?
>>
>> We would not just do so if they're empty, we would just generally
>copy the file
>> via shared buffers, instead of copy_file(). But we'd get the file
>size
>> from the filesystem (which is fine, we make sure it is correct during
>> replay).
>
>So, this suggestion is basically implementing the reverse operation of
>GetRelationPath() to be able to rebuild a RelFileNode from scratch and
>then look at the shared buffers needed. Isn't it a bit brittle for
>back-branches? RelFileNode stuff is available easily through records
>when replaying individually FPIs, but not really in this code path.
Oh, sorry. In definitely not thinking about doing this for the back branches. That was more musing about a way to
optimizethis.
Andres
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